I want to have a room, like a few I know, without any windows. Not really for protecting guitars, which is good and really the only way to control temperature and humidity perfectly, but also for recording. Sometimes even with the best baffling, there's no easy or pretty way to shield sound of music from the street when you have a room with a window. You can cut bleed from a door pretty well, double baffled door, but there's no way to do that with window.
With heavy hitting drummers who think they are John Bonham or bass guitars backed by real watts, there's no effective way to completely shut out sound bleeding out other than a windowless room. Sometimes you also want to be able to turn it up but also not advertise to would be thiefs that there's expensive gear inside. I don't care if you have guns or pit bulls, if you advertise you have gear with bleed into the street, some meth head will find a way in and rip you off. Maybe it's a California thing, but stolen gear is found in every used music store since the cops simply don't care or can't do anything even if they did care. Trying to tell a cop that you had an electric guitar stolen is like telling them you want to report somebody who stole your bong.
I have seen so many of the better studios in shady neighborhoods and it's amazing how not a decibel gets out into the street. Whether it's in Van Nuys or NYC, the whole idea of unmarked buildings with no windows but platinum records on the wall inside is the model I kind of like.
And it the windowless room still speaks to my laziness of taking stuff out of cases and then putting them back in. Why not have a room that you can proudly have your old school Martin permanently making its home on the studio couch? Sure that old Martin sounds better because it has a thinner top and much more delicate bracing, and that its tone cuts through because of a solid and super resonant neck without the aid of a truss rod, but its also those features which makes precious stuff like this usually unable to live outside a case for more than a few hours at a time.
Unfortunately, I live in a neighborhood that is extremely restrictive as to making changes on a house and/or yard, that a windowless room is out of the question. To give you an idea, river rock used to be one of the only few choices allowed for landscaping but then all river rock, even in backyard, became forbidden otherwise the city would give an order to remove it at owner's cost!
My old teacher had a drool-worthy vintage Gibson L5 with dual original PAFs in it and he would pull it out and jam on a piece with us, but if he got up and walked around the room and helped us with guitar or horn parts, he put it back in case. If he went to play again, he pulled it out again. Even though the class was at night and no sun was coming in, the temperature of that classroom varied wildly from week to week and even from start of class right after sunset until 9 pm. Being a professional, local gigging musician (read: poor) and not used to the money many others had in non-musical jobs, that guitar represented a whole year, or two, of earnings. A Gibson L5 from the McCarty days is worth more than most of our entire collections. The top was hand carved solid spruce so thin you could almost see through it but it had the traditional super taught 14 or 15 gauge strings that such a guitar was strung with in a big band, but it made a lowly ES-175 sound like a toy, tone-wise.
It can't be overstated how top gear (usually far more delicate than normal gear) needs to be protected and is subject to even small changes in temperature and humidity. The great pianist Horowitz used to travel with a piano tuner tech who would always tune the piano no more than an hour before the show. If a piano was tuned more than an hour earlier, he could easily hear it. Being subject to much stronger construction, imagine how mutable a nice guitar like an L5 is. It's kind of nice we here mostly like solidbody guitars with truss rods and slinky strings because the abuse from weather and bad guitar hygiene is much more easily forgiven. That being said, I do miss my '47 Martin.